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1. Field of the Invention
The apparatus and method of the present invention relates to wireline operations in the recovery of oil and gas. More particularly, the present invention relates to a method and apparatus for controlling well pressure while undergoing wireline operations on subsea blowout preventers on the subsea floor.
2. General Background of the Invention
In conducting wireline operations, many types of tools are positioned on the lower end of a wireline, which is a steel cable or the like, lowered into the well bore in order to undertake certain tests downhole. Because in the past there has been difficulties in undertaking wireline work with the potential hazard of blowouts in the well, there has been developed and patented by Harper Boyd, a side entry sub assembly which is patented under U.S. Pat. No. 4,681,162 and reissued under U.S. RE 33,150. This patented device, which is placed below the top drive on the rig floor, includes a side entry portion which enables the wireline to extend through the side entry passage and into the main passage and downward into the drill string. Although the use of the side entry sub is common for drilling, the system has never been applied safely on subsea blowout preventers which are located in deep water, since it controlling the well pressure at deep depths is very difficult. In deep waters of the Gulf of Mexico, there would be provided a floating subsea riser which would extend from the rig floor, on the Gulf surface, to the blowout preventers on the floor of the Gulf, sometimes some 4,000 to 7,000 feet in distance. It would be quite impractical to run a high-pressure line from the rig floor to the BOP stack on the Gulf floor to tie into the hydril so that one could pressure test the wireline. The BOP""s need to be pressure tested, but the riser cannot take high pressure tests above the blowout preventers, or it would rupture and expel hydrocarbons into the Gulf waters. So, there is a need to be able to conduct subsea wireline operations in deep waters under pressure so that in the event a well would xe2x80x9ccome inxe2x80x9d during the operations, the blowout would not reach the riser to the rig floor to avoid rupture of the floating subsea riser and a major catastrophe.
The apparatus and method of the present invention solves the problems in a simple and straightforward manner. What is provided is a method for conducting wireline operations in a deep, subsea location, which includes providing a rig on the surface of a body of water, having a riser extending from the rig floor to the floor of the deep body of water; a hydril positioned on the end of the riser on the sea floor; a plurality of blowout preventers positioned below the riser to prevent a blowout into the riser; a wireline subsea blowout preventer control head assembly (the assembly) lowered into the riser to the level into the hydril; pressuring off the assembly by the riser and blowout preventers; lowering a wireline down the riser into the assembly so that the tool may be lowered beyond the blowout preventers to conduct wireline operations; providing a means to pressure off the assembly so that should a blowout occur during wireline operations, any pressure would be prevented from entering the riser, but would be contained by the assembly.
Therefore, it is a principal object of the present invention to provide a system for conducting wireline operations in a subsea conditions at the floor of the seabed, so as to prevent any undue pressure from rupturing the riser between the rig floor and the subsea floor.
It is a further object of the present invention to provide a method of conducting wireline operations deep within a subsea conditions, without subjecting the riser between the rig floor and the seabed to blowout pressures;
It is a further object of the present invention to provide a wireline subsea blowout preventer control head assembly system used in subsea conditions for allowing wireline work to be conducted at the sea floor, under pressure, so as to allow pressure testing of components of the system without fear of compromising the integrity of the riser which may cause a catastrophic oil or gas spill into the body of water.